This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Growth failure is a significant manifestation of acquired prolonged hypothyroidism, resulting in permanent loss in height and only seventy percent catch-up growth is achieved with thyroxine replacement. Patients treated with thyroxine at a mean chronologic age of 11 years have adult heights approximatley two standard deviations below the mean-final hights and are lower than the mid-parental and predicted adult heights. The concomitant administration of growth hormone to restore growth rate, in addition to a Gonadrotrophin releaseing (GNRHa) to arrest epiphysial maturation, offers the possibility of improving final height prognosis. This randomized study will evaluate the long-term effect of concomitant administration of growth hormone and GNRHa in addition to thyroxine vs. standard therapy of thyroxine alone on th efinal height of adolescents with prolonged juvenile hypothyroidism. In addition, a cohort of patients with short duration of hypothyroidism will also be followed to delineate the effects of short vs. prolonged hypothyroidism on growth.